Production of nitrogen trifluoride



United States Patent 3,067,111 PRODUCTION OF NITROGEN TRIFLUORIDE MartinSchmeisser and Friedo Huber, Aachen, Germany; said Huber assignor tosaid Schmeisser No Drawing. Filed Dec. 4, 1958, Ser. No. 778,060 Claimspriority, application Germany Dec. 16, 1957 a 3 Claims. (Cl. 204-59) Thepresent invention relates to an improved and convenient process ofproducing nitrogen trifluoride.

Nitrogen trifluoride, NF was produced by O. Rufi, I. Fischer and F.Luft, Z. anorg. allg. Chem. 172, 417 (1928), by electrolysis of NH F inanhydrous hydrogen fluoride. However, this process produces only verysmall yields; besides, it is not always reproducible and is accompaniedwith pufis and explosions.

A more advantageous process of producing nitrogen trifluoride is theelectrolysis of pyridine in anhydrous hydrogen fluoride, wherein NF isformed as by-product (this process is described by J. H. Simons, J.Electrochem. Soc. 95, 47 (1949), and in US. Letters Patent No.2,519,983). However, this process i not suitable in the production of NFinsofar as large amounts of CF are simultaneously formed as anotherlay-product and, because of the substantially similar physical andchemical properties (B.P. NF 129 C., B.P. CF 128 C.), it is possibleonly with great difliculty to separate CE; from NF It is the principalobject of the present invention to do away with the aforesaiddisadvantages and to provide a novel and economic process of producingnitrogen trifluoride in high purity and good yield.

Further objects will become apparent as the following descriptionproceeds.

In accordance with the present invention it has been found that nitrogentrifluoride is produced by electrolysis of a solution of urea inanhydrous hydrogen fluoride.

The new process produces NF in high purity and good yield while avoidingthe disadvantage associated with the aforesaid prior art processes. Theprocess of the invention is preferably carried out at a voltage of about6 volts using a current of about 20 amperes or about 30 amperes persquare decimeter. Besides slight amounts of CE; and 0P as well as ofhigh molecular weight compounds containing C and F, the new processproduces appreciable quantities of N COF and CO as by-products which caneasily be separated from the NF which is obtained in large quantities.About 50 ICC percent of the nitrogen present in the. starting materialis obtained in form of NF Nitrogen trifluoride can be used as adielectric as well as a compound yielding fluorine under appropriateconditions.

The invention is further illustrated by the following example withoutbeing restricted thereto.

Example 200 grams of urea are dissolved at -10 C. in about 2 litres ofanhydrous hydrogen fluoride to give a solution of CO(NH .2HF. Thesolution is electrolyzed at the same temperature (-10 'C.) whileapplying a voltage of 6 volts and a current of about 20 amperes. Theresulting volatile reaction products are passed through tubes containingsolid potassium fluoride in order to remove any entrained hydrogenfluoride, and then Washed with aqueous alkaline Na S- O -so1ution inorder to remove COF CO and OF Any entrained water vapor (originatingfrom the Na S O solution) is retained by being passed through a trapcooled to a temperature of -78 C. The crude product obtained isfractionated in high vacuum between -183 and 196 C., distilled andthereby liberated from all the aforesaid impurities (except -l percentCR We claim:

t1. Process for the production of nitrogen trifluoride, which compriseselectrolyzing a current-conducting solution of urea in anhydroushydrogen fluoride at a temperature and pressure at which a liquid stateis maintained and at a cell voltage sutficient to cause the pro ductionof nitrogen trifluoride at a useful rate, and recovering the nitrogentrifluoride formed.

\2. Process according to claim 1, in which the electrolyzing is effectedat a temperature of about 10 C. and a voltage of about 6 volts and acurrent of about 30 amperes per square decimeter.

3. Process according to claim 1, in which the electrolyzing is effectedat a temperature of about -10 C. and a voltage of about 6 volts and acurrent of about 20 amperes per square decimeter.

Simons et al.: Journal Electrochemical Society, vol. (February 1949),pages 47-67.

1. PROCESS FOR THE PRODUCTION OF NITROGEN TRIFLUORIDE, WHICH COMPRISESELECTROLYZING A CURRENT-CONDUCTING SOLUTION OF UREA IN ANHYDROUSHYDROGEN FLUORIDE AT A TEMPERATURE AND PRESSURE AT WHICH A LIQUID STATEIS MAINTAINED AND AT A CELL VOLTAGE SUFFICIENT TO CAUSE THE PRODUCTIONOF NITROGEN TRIFLUORIDE AT A USEFUL RATE, AND RECOVERING THE NITROGENTRIFLUORIDE FORMED.